摘要:

A simple experimental approach has been employed to obtain thermochemical parameters for cation vacancy formation and migration in the AlGaAs heterostructure system. Cation vacancies are injected into the free surface by annealing under an arsenic-rich ambient. Their presence is detected by monitoring the local rate of Al–Ga interdiffusion at imbedded quantum well markers. The sample is unusually thick allowing us to separately identify contributions from the vapor, epilayer, and substrate phases. The entropies and enthalpies of vacancy formation and migration are(5.2±5.7) kBand(1.8±0.5) eVand(11.3±4.4) kBand(3.3±0.4) eV,respectively. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122874

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Infrared spectroscopy and secondary ion mass spectrometry are used to elucidate the mechanism by which co-implantation of He with H facilitates the shearing of crystalline Si. By studying different implant conditions, we can separate the relative contributions of damage, internal pressure generation, and chemical passivation to the enhanced exfoliation process. We find that the He acts physically as a source of internal pressure but also in an indirectchemicalsense, leading to the reconversion of molecularH2to bound Si–H in “VH2-like” defects. We postulate that it is the formation of these hydrogenated defects at the advancing front of the expanding microcavities that enhances the exfoliation process.

ISSN:0003-6951    

DOI:10.1063/1.122875

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Intersubband electroluminescence has been investigated in a quantum cascade structure based on vertical transition designed for far-infrared(&lgr;=88 &mgr;m)emission. A narrow luminescence peak with a full width at half maximum of 0.7 meV is measured at low excitation currents(30 A/cm2) and low temperature(T=5 K).The electroluminescence efficiency exhibits a strong temperature and current dependence, consistent with an interplay between electron–electron and optical phonon scattering. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122895

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A fine structure was discovered in the low-energy peak of the secondary electron emission spectra of the diamond surface with negative electron affinity. We studied this structure for the (100) surface of the natural type-IIb diamond crystal. We have found that the low-energy peak consists of a total of four maxima. The relative energy positions of three of them could be related to the electron energy minima near the bottom of the conduction band. The fourth peak, having the lowest energy, was attributed to the breakup of the bulk exciton at the surface during the process of secondary electron emission. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122876

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on threefold-stacked vertically aligned InP/GaInP quantum dot injection lasers emitting in the visible part of the spectrum (690–705 nm) with a low threshold current density ofjth=172 A/cm2at 90 K showing a thermally activated increase towards higher temperatures. We derived an activation energy for this behavior, which is found to be just one half of the energetic distance between the dot transition energy and the wetting layer band gap. Thus, we identify thermal evaporation of carriers out of the dots and into the wetting layer states as the process responsible for the increase in the threshold current. The nonradiative carrier lifetime in the wetting layer(&tgr;nrWL)is estimated to be approximately 250–400 ps. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122877

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Ambipolar carrier transport properties in different phases of a liquid-crystalline photoconductor, 2-(4-octylphenyl)–6-n-butoxynaphthalene, were investigated by a time-of-flight technique. Carrier mobilities were increased stepwise when phase transition took place as the temperature decreased. The smecticEphase in the range of 55–125&hthinsp;°C exhibited nondispersive ambipolar carrier transport with an anomalous high carrier mobility of1.0×10−2 cm2/V&hthinsp;s,while the smecticAphase between 125 and 129&hthinsp;°C had similar carrier transport with a smaller mobility of4×10−4 cm2/V&hthinsp;s.In contrast to the crystalline phase, structural defects in the smecticEphase, which were obvious under microscopic observation with polarized illumination, did not deteriorate the carrier transport properties. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122896

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Lattice strain relaxation in InAs/GaSb heterostructures was investigated by x-ray diffraction. Two types of structures, grown by molecular beam epitaxy, are compared. In the first, GaSb buffer layers were grown on GaAs substrates, followed by 0.05–1.0 &mgr;m thick InAs layers. In the second, InAs layers were grown directly on GaSb substrates. For a given thickness, the InAs layers retain significantly more strain when grown on GaSb substrates, reflecting the lower threading dislocation density in the GaSb substrates relative to the GaSb buffer layers grown on GaAs.

ISSN:0003-6951    

DOI:10.1063/1.122878

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A highlyefficient electronemitting diode with a flat emission surface has been fabricated using a 600 nm single-crystalline diamond film homoepitaxially grown on high-pressure synthesized (100) diamond by means of chemical-vapor deposition and ion-implantation techniques. The emitter contains a buried injection electrode layer and a hydrogenated diamond surface. When driving voltages ranging from 0.3 to 1.1 kV were applied between them, veryefficient electronemissions were observed. The emission efficiency, defined as the ratio of the emission current to the injection diode current, reached 100&percent; for emission currents on the order of10−7 Aand did not significantly depend on the currents. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122879

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A phenomenon was discovered that leads to the selective detection of abrupt increases in the temperature of conductive composite thin films consisting of conductive ceramic fillers and an insulating polymer matrix. Examining the heating rate dependence of the positive-temperature–coefficient-of-resistivity (PTCR) effect provided information about this intelligent phenomenon. The anomalous PTCR effect was observed above0.3 °C min−1for all the prepared films. However, the magnitude of the anomaly decreased when the heating rate decreased below0.1 °C min−1,and when the heating rate further decreased below0.04 °C min−1,the anomalous resistivity–temperature relationship disappeared. The results suggest that these thin films can selectively detect abrupt increases in temperature, which could lead to an intelligent mechanism. Our results also suggest a PTCR mechanism, in which the expansion of crosslinked polymers in the thermodynamic nonequilibrium state essentially produces the anomaly. ©1998 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.122880

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Epitaxialn-GaNwas irradiated with 5.4-MeV He ions. Capacitance–voltage(C–V)measurements showed that 5.4-MeV He ions remove free carriers at a rate of6200±300 cm−1in the first micron below the surface. Deep level transient spectroscopy (DLTS) revealed that, in addition to the radiation-induced defects previously detected by DLTS at 0.18–0.20 eV below the conduction band, He-ion irradiation introduced two additional prominent defects, ER4(EC-0.78 eV)and ER5(EC-0.95 eV)at rates of1510±300and3030±500 cm−1,respectively. Capture cross-section measurements revealed that electron capture kinetics of ER5 is similar to that of a line defect. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122881

出版商:AIP    

年代:1998

数据来源: AIP